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In the study published in the journal Proceedings of the National Academy of Sciences (PNAS), researchers from Caltech have demonstrated that Barkhausen noise can be generated through quantum mechanical effects in addition to classical methods. Barkhausen noise occurs when tiny magnets within a material flip in groups, creating a crackling sound. The research represents an advancement in fundamental physics and has implications for the development of quantum sensors and other electronic devices.

Traditionally, the flipping of these magnets, or spins, occurs through thermal activation, where particles gain energy to overcome an energy barrier. However, the researchers found that these flips can also occur through quantum tunneling, where particles can pass through the barrier without climbing over it. This quantum effect allows the flips to happen without the need for classical energy requirements, leading to macroscopic changes in the material.

In addition to quantum tunneling, the researchers discovered a co-tunneling effect, where groups of tunneling electrons communicate with each other to drive the electron spins to flip in the same direction. This collaborative effect was unexpected and highlights the complex behavior of electron spins in materials under quantum influence. By studying these phenomena in a pink crystalline material at extremely low temperatures, the team observed voltage spikes indicating the flipping of electron spins, similar to Barkhausen’s original experiment in 1919.

The experiment showed that magnetic avalanches could occur even without classical effects, and these effects were found to be insensitive to changes in temperature. The researchers concluded that quantum effects were responsible for the observed sweeping changes in the material. This demonstration of quantum behavior in materials with trillions of spins highlights the coherence of microscopic objects displaying quantum mechanical effects on a macroscopic scale, contributing to a deeper understanding of quantum phenomena.

The study builds on previous research from the lab of Thomas F. Rosenbaum, focusing on how tiny quantum effects can lead to larger-scale changes. By studying the element chromium, the researchers showed how different types of charge modulation can interfere quantum mechanically at different length scales. This new understanding of quantum behavior in simple systems sheds light on the potential for studying quantum effects on a macroscopic level and highlights the complexity of quantum interactions in materials.

Funded by the U.S. Department of Energy and the National Sciences and Engineering Research Council of Canada, the study titled “Quantum Barkhausen noise induced by domain wall cotunneling” brings together a team of researchers to explore the intersection of classical and quantum effects in magnetism. Led by Christopher Simon and co-authored by Daniel Silevitch and Philip Stamp, the research offers valuable insights into the behavior of electron spins in materials under the influence of quantum mechanics.

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